The present invention relates to a circuit arrangement for determining the angular position of a rotating member, particularly of a rotating shaft of an internal combustion (or I.C.) engine, by means of a counter and a sensor which detects the angular position of the shaft. The output signal of the sensor is fed to an evaluating circuit whose resolution of the detected angular position is greater than that of the sensor. A synchronizing circuit provides synchronization or an independent time control between the output signal of the sensor and the concurrent high resolution angle of rotation delivered by the evaluating circuit.
The determination of the angular position of a rotating member is a task which frequently occurs in the art. For example, in the motor vehicle technology it is required for the control of an internal combustion engine to determine the angular position of its cam shaft or crankshaft so that a control apparatus could perform its controlling function at correct time points.
Known are systems for measuring angle rotation which include a sensor consisting of two transmitters or pickups. The pickups are displaced by an angle relative to each other and determine the respective angular positions of a rotating member by scanning thereon markings or the like which are distributed around the circumference of the member. The disadvantage of this prior art system is the fact that the resolution of the measuring signal is limited by the available number of the markings.
From the U.S. Pat. No. 3,830,207 a control device for the ignition and fuel injection of an I.C. engine is known wherein markings on the cam shaft and on the crankshaft are scanned by sensors. The output signals of the sensors are applied to an evaluating circuit. The sensor assigned to the crankshaft includes two transmitters or pickups which form one with the other an angle of 30 degrees. By the provision of two sensors and due to the fact that the cam shaft rotates at half the speed of the crankshaft it is possible to limit the errors or tolerances in the determination of the angular position of the crankshaft inasmuch as the maximal error is always between the respective maximum errors of the crankshaft and the cam shaft. Owing to the smaller rotary speed of the cam shaft an error which at the crankshaft may amount for example to 10 degrees is reduced to 5 degrees. To that extent the prior art arrangement provides a relatively precise determination of ignition- and fuel injection time points of the I.C. engine. Nevertheless, there is still the need to improve the accuracy.
The prior art circuit arrangements of the above described kind are available as the so-called `Tachogenerator Outputs` and make a relatively exact determination of the angular position possible.